The present invention relates to a flow improver for crude and distillate oils which is recovered from crude oil by extraction by means of supercritical gases.
Crude oils, residue oils, oil distillates, such as, for example, diesel fuel, mineral oils, lubricating oils, hydraulic oils, etc., contain, depending on their origin or the nature of their processing, varying proportions of n-paraffins and asphaltenes, which represent particular problems since they crystallize out or agglomerate on a reduction in the temperature and can thus result in impairment of the flow properties of these oils. This impairment of the flow properties of the oils is known as xe2x80x9csolidificationxe2x80x9d of the oil. The pour point is the standardized term for the temperature at which an oil, for example mineral oil, diesel fuel or hydraulic oil, just stops flowing on cooling. However, the pour point is not identical with the so-called flow point. The flow point is a non-specific term, not covered by standards, for the temperature at which a solid starts to flow under given measurement conditions. Due to the impairment in the flow properties, tanks, pipelines, valves or pumps may block, for example during transport, during storage and/or during processing of these oils, in particular in the case of paraffin-containing oils, which are difficult to inhibit. In addition, paraffin precipitations require increased pressures during re-start of pipelines (yield point).
Particular difficulties occur in practice if the wax appearance temperature (WAT) and in particular the inherent pour point of these oils is above the ambient temperature, in particular at 20xc2x0 C. or above. In view of decreasing world oil reserves and increasing exploitation of deposits that yield crude oils with high inherent pour points, the recovery and transport of problem oils of this type is achieving ever-greater importance.
Flowability can be restored or maintained using a number of measures of a thermal or mechanical nature, for example scraping the crystallized paraffin off the inside wall of pipes by regular pigging, heating of entire pipelines, or flushing processes with solvents. It is undoubtedly more elegant to combat the causes of the phenomenon by addition of flow improvers, which are also known as pour point depressants or paraffin inhibitors. A lowering of the pour point to values below the respective ambient temperature, in particular to values of about 10xc2x0 C. or below, is generally advantageous here.
The way in which these flow improvers work is generally explained as being that they inhibit crystallization of paraffins and asphaltenes or co-crystallize with the paraffins or paraffin/asphaltene adducts and thereby result in the formation of smaller paraffin crystals, which are no longer able to aggregate and form a network which impairs flowability. The consequence is a lowering of the pour point and maintenance of the flowability of the oil at low temperature. The effectiveness of the flow improvers is dependent both on their chemical structure (composition) and on their concentration.
The flow improvers disclosed in the prior art are generally synthetic polymers, which usually contain structural units of ethylene and structural units of unsaturated carboxylic acid esters.
The disadvantage of these flow improvers from the prior art consists in their expensive preparation and their lack of general applicability. Thus, it is generally necessary to re-formulate flow improvers for particular uses.
Besides the said synthetic polymers, the prior art also discloses attempts to prepare cold-flow improvers for oils directly from crude oil or oil products.
U.S. Pat. No. 3,523,071 discloses that the heavy products of a shale oil which has already been subjected to visbreaking are effective pour point depressants for hydrodenitrated shale oil. On the other hand, however, these products have no effect on crude shale oil.
U.S. Pat. No. 3,532,618 discloses the preparation of asphaltenes which act as pour point depressants in shale oil by hydrovisbreaking of shale oil followed by deasphalting of the hydrovisbreaker product stream.
U.S. Pat. No. 4,201,658 likewise discloses a process for lowering the pour point of shale oils. Here, the asphaltenes of a thermally treated shale oil were employed as pour point depressants in relatively high concentrations of up to 12% by weight.
U.S. Pat. No. 4,728,412 discloses the flow-improving action of tar sand bitumen which has been subjected to various treatments in crude oils having a high pour point. Here too, relatively high amounts of up to 60% by weight are used as pour point depressants.
It is evident from all these documents that high concentrations were necessary hitherto for paraffin inhibition using pour point depressants based on components present in petroleum. In addition, all pour point depressants disclosed in these processes first have to be produced by treatment of the crude oils (which are shale oils) at high temperatures.
K. Zosel, Angew. Chem. 90 (1978), pp. 748-755, discloses a process for the deasphalting of top oils. This process uses extraction with supercritical gases. However, the effectiveness of products obtained therefrom is not disclosed.
WO-00/52118 discloses a process for the refining of oils, including petroleum, which is characterized by supercritical extraction of the oils. A flow-improving action of extraction residues is not disclosed.
The object of the present invention is to provide a flow improver which represents an alternative to the synthetic polymers of the prior art. This flow improver should be inexpensive to produce with no additional use of resources compared with the prior art. It should also be effective in smaller amounts than the prior-art pour point depressants based on components present in petroleum and should be producible without heat treatment, including from crude oils.
Surprisingly, it has now been found that flow improvers based on components present in petroleum can be obtained by extraction of crude oils by means of supercritical gases.
The invention thus relates to an additive for improving the cold-flow properties of crude and distillate oils, where the additive is obtainable by extraction of crude oil with supercritical gas.
The invention furthermore relates to fuel oils which comprise the additives described above.
The invention furthermore relates to the use of an extraction residue obtainable by extraction of crude oil by means of supercritical gases as cold-flow improvers for crude and distillate oils.
The invention furthermore relates to a process for the preparation of an additive which improves the cold-flow properties of crude and distillate oils by subjecting crude oil to extraction by means of supercritical gases, and isolating the resultant extraction residue.
Separation of substances by means of supercritical gases (supercritical fluid extraction, SFE) is a well known method in the prior art and its principles will not be discussed here. It is disclosed by way of example in xe2x80x9cAngewandte Chemie, Volume 90 (1978), Issue 10, pages 747-761xe2x80x9d, which is expressly incorporated herein by way of reference.
The additives according to the invention can be obtained from any desired crude oils. The crude oils are preferably conventional crude oils. A preferred embodiment uses resin-rich crude oils which have resin contents of at least 0.5% by weight, in particular at least 5%by weight. The resin contents of the crude oils may be, for example, up to 30% by weight, in particular cases even up to 50% by weight.
The extraction is preferably carried out with nonpolar or slightly polar, low-molecular-weight gases having molecular weights of up to 200, in particular up to 100 units, or mixtures thereof. Examples of suitable gases are carbon dioxide, C1-C5-alkanes, C2-C5-alkenes and C1-C3-fluoroalkanes. Preference is given to CO2, ethylene or propane.
The extraction is generally carried out at pressures of from 50 to 500 bar and at temperatures of from 30 to 150xc2x0 C., preferably up to 100xc2x0 C. It should be noted here that the pressure and temperature must be selected so that the extractant is a supercritical gas. In addition to the extractant, an entrainer can be used during the extraction. Entrainers are substances which, when added in small amounts of from 2 to 15 mol %, preferably up to 10 mol %, based on the extractant, improve the yield and selectivity of supercritical extraction. Suitable entrainers are weakly polar or nonpolar organic compounds, such as, for example, isooctane or toluene, or mixtures thereof.
The extraction residue is isolated by removal of the extractant loaded with the extract. It is also possible to effect the isolation by adsorption of the extract onto suitable adsorbents or by changing the temperature, as a result of which the extract is deposited elsewhere from the extractant, and the extractant can be brought into renewed contact with the extraction residue. In a preferred embodiment, the process is carried out in a circulation apparatus with continuous extract deposition.
The direct extraction residue (additive) is suitable for improving the cold-flow properties of crude and distillate oils. In order to increase the effectiveness of the additives according to the invention, the extraction residue can be further processed.
In a preferred embodiment of the invention, the extraction residue obtained from crude oil is extracted with a polar solvent. Suitable polar solvents are C3- to C10-alcohols, esters of carboxylic acids having from 2 to 5 carbon atoms with alcohols having from 1 to 5 carbon atoms, in particular esters of acetic acid, such as ethyl acetate. The residue from this extraction is then re-extracted with a nonpolar solvent. Suitable nonpolar solvents are aliphatic solvents, preferably alkanes which are liquid at room temperature, in particular n-pentane. The extract obtained with the nonpolar solvent is the purified flow improver (additive) with increased effectiveness.
The additives according to the invention are suitable for improving the cold-flow properties of crude oils, distillate oils or fuel oils as well as lubricating oils. The oils may be of mineral, animal or vegetable origin.
Besides crude oils and residue oils, particularly suitable fuel oils are middle distillates. The term middle distillates is applied, in particular, to mineral oils which are obtained by distillation of crude oil and boil in the range from 120 to 320xc2x0 C., such as, for example, kerosene, jet fuel, diesel and heating oil. They may also comprise proportions of alcoholic fuels, such as, for example, ethanol and methanol, or alternatively biofuels, such as, for example, rapeseed oil or rapeseed oil acid methyl ester. In particular, they are effective in oils whose GC-determined content of n-paraffins which have chain lengths of 22 carbon atoms or more is at least 1.0 area-%, in particular greater than 1.5 area-%, especially 2.0 area-% or more. The 90% distillation point of the oils according to the invention is preferably above 345xc2x0 C., in particular above 350xc2x0 C., especially above 355xc2x0 C. These oils preferably have cloud points above xe2x88x9210xc2x0 C., in particular above xe2x88x925xc2x0 C.
The additives can be used alone or alternatively together with other additives, for example with dewaxing aids, conductivity improvers, antifoams, dispersion aids, demulsifiers, asphaltene inhibitors, gas hydrate inhibitors, scale inhibitors, paraffin dispersants, corrosion inhibitors, antioxidants, lubricity additives, dehazers or sludge inhibitors.
The additive components can be added to the oils to be treated with additives together as a concentrate mixture in suitable solvents or also separately.
The additives according to the invention are added to mineral oils or mineral oil distillates in the form of emulsions, solutions or dispersions. The additives according to the invention can also be added to the oils in the form of solid granules or pellets, which is preferably the case in the recovery of crude oil. These solutions or dispersions preferably comprise from 1 to 90% by weight, in particular from 5 to 80% by weight, of the mixtures. Suitable solvents or dispersion media are aliphatic and/or aromatic hydrocarbons or hydrocarbon mixtures, for example gasoline fractions, kerosene, decane, pentadecane, toluene, xylene, ethylbenzene or commercial solvent mixtures, such as solvent naphtha, (copyright)Shellsol AB, (copyright)Solvesso 150, (copyright)Solvesso 200, (copyright)Exxsol, (copyright)ISOPAR and (copyright)Shellsol D grades. The solvent mixtures mentioned comprise various amounts of aliphatic and/or aromatic hydrocarbons. The aliphatics may be straight-chain (n-paraffins) or branched (isoparaffins). Aromatic hydro-carbons may be monocyclic, bicyclic or polycyclic and may optionally carry one or more substituents. Mineral oils or mineral oil distillates whose Theological properties have been improved by the additives according to the invention comprise from 0.001 to 2% by weight, preferably from 0.005 to 0.5% by weight, of the additives, based on the distillate.
For the production of additive packages for specific problem solutions, the additives according to the invention may also be employed together with one or more oil-soluble co-additives, which even on their own improve the cold-flow properties of crude oils, lubricating oils or fuel oils. Examples of co-additives of this type are copolymers of ethylene and ethylenically unsaturated esters, comb polymers, alkylphenol-aldehyde resins and polar compounds which effect paraffin dispersion (paraffin dispersants).
Thus, the additives according to the invention can be employed in the form of a mixture with alkylphenol-formaldehyde resins. In a preferred embodiment of the invention, these alkylphenol-formaldehyde resins are those of the formula 
in which R1 is C4-C50-alkyl or -alkenyl, [Oxe2x80x94R2] is ethoxy and/or propoxy, n is a number from 5 to 100, and p is a number from 0 to 50. Paraffin dispersants reduce the size of the paraffin crystals and have the effect that the paraffin particles do not settle out, but instead remain colloidally dispersed with significantly reduced sedimentation volition. Paraffin dispersants which have proven successful are oil-soluble polar compounds containing ionic or polar groups, for example amine salts and/or amides, which can be obtained by reaction of aliphatic or aromatic amines, preferably long-chain aliphatic amines, with aliphatic or aromatic mono-, di-, tri- or tetracarboxylic acids or anhydrides thereof. Other paraffin dispersants are copolymers of maleic anhydride and xcex1,xcex2-unsaturated compounds, which can, if desired, be reacted with primary monoalkylamines and/or aliphatic alcohols, the products of the reaction of alkenylspirobislactones with amines, and products of the reaction of terpolymers based on xcex1,xcex2-unsaturated dicarboxylic anhydrides, xcex1,xcex2-unsaturated compounds and polyoxyalkylene ethers of lower unsaturated alcohols. Alkylphenol-formaldehyde resins are also suitable as paraffin dispersants.
The mixing ratio (in parts by weight) of the additives with paraffin dispersants is in each case from 1:10 to 20:1, preferably from 1:1 to 10:1.
In a further preferred embodiment of the invention, the additives according to the invention are used in the form of a mixture with ethylene copolymers.
Ethylene copolymers of this type preferably contain from 8 to 20 mol %, in particular from 9 to 13 mol %, of at least one vinyl ester, such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl hexanoate, vinyl octanoate, vinyl neononanoate and neodecanoate, a C1-C30-alkylvinyl ester and/or C1-C30-alkyl (meth)acrylate. They furthermore preferably comprise 1-6 mol % of at least one olefin having 3-8 carbon atoms, such as propene, butene, isobutene, diisobutylene, pentene, hexene, 4-methylpentene, norbornene or octene. It is furthermore also possible to employ mixtures of different flow improvers having a different quantitative (for example comonomer content) and/or qualitative composition (type of the copolymers/terpolymers, molecular weight and degree of branching).
According to a preferred embodiment of the invention, the additives according to the invention are employed in the form of a mixture with ethylene-vinyl acetate-vinyl neononanoate terpolymers or ethylene-vinyl acetate-vinyl neodecanoate terpolymers. Besides ethylene, the terpolymers of vinyl neononanoate or vinyl neodecanoate comprise from 10 to 35% by weight of vinyl acetate and from 1 to 25% by weight of the respective neo compound.
In a further preferred embodiment of the invention, the additives according to the invention are employed with terpolymers which, besides ethylene, comprise 10-35% by weight of vinyl esters and from 0.5 to 20% by weight of olefins, such as, for example, diisobutylene, hexene, 4-methylpentene and/or norbornene.
The mixing ratio of the additives according to the invention with the above-described ethylene-vinyl acetate copolymers or the terpolymers of ethylene, vinyl acetate and the vinyl esters of neononanoic or neodecanoic acid or of ethylene, vinyl esters and olefins is (in parts by weight) from 20:1 to 1:20, preferably from 10:1 to 1:10. The mixtures of the additives according to the invention with the said copolymers are particularly suitable for improving the flowability of middle distillates.